a. Field of the Invention
This invention is directed to direct view electro-optical displays, as for example, a liquid crystal display, and more particularly, relates to the field of backlit displays particularly adapted for military and avionics applications which are specially designed to present a bright, uniform distribution of light in a low profile assembly.
b. Description of Related Art
There has been an extensive ongoing effort to provide large, full color display systems which do not rely upon the conventional cathode ray tube. See, for example, "Flat-Panel Displays," Scientific American, March 1993, pages 90-97. In systems such as television receivers, computer monitors, avionics displays, aerospace displays and military-related displays, the elimination of cathode ray tube technology is desirable. See for example U.S. Pat. Nos. 4,843,381, 5128,783 and 5,161,041 for a discussion of the disadvantages of cathode ray tube technology.
Display devices, as for example, projection display devices, off screen display devices and direct view displays are known. See for example, EPO 0 525 55 A1; U.S. Pat. Nos. 4,659,185, 5,132,830 and 5,159,478; and Japanese Publication Nos. 245106 and 42241. Such displays are used in a wide range of applications including televisions, computer monitors, avionics displays, aerospace displays, automotive instrument panels and other devices that provide text, graphics or video information. These types of displays can replace conventional cathode ray tube displays and offer advantages such as lower profile, reduced weight and lower power consumption.
One display which can eliminate the shortcomings of a cathode ray tube is the flat panel liquid crystal display (LCD). LCDs are typically either reflective or transmissive. A reflective display is one which depends upon ambient light conditions in order to view the display. A transmissive LCD requires an illuminating means or backlight to ensure that the display image is as bright as possible. LCDs, however, suffer from a number of inherent disadvantages. For example, at high viewing angles (large angles from the direction normal to the surface of the display), LCDs exhibit low contrast and changes in visual chromaticity as the viewing angle changes.
The characteristics of the backlighting scheme are very important to both the quality of the image displayed by the matrix array of picture elements of the LCD and the profile of the display. See U.S. Pat. Nos. 5,128,783 and 5,161,041 for a discussion of the deficiencies in past backlighting configurations.
Accordingly, there exists a need in the flat panel electro-optical display field for an improved lighting/optical arrangement which provides an efficient, bright and uniform image of high contrast and is capable of being viewed over a wide viewing angle, while maintaining a narrow profile.